A false start is called when "an offensive player who has assumed a set position charges or moves in such a way as to simulate the start of a play, or if an offensive player who is in motion makes a sudden movement toward the line of scrimmage." (NFL Rules 7.4.2)

Illegal motion (which is not a dead-ball foul) is called when an offensive player is moving forward at the snap or is never set for one second at any point before the snap (NFL Rules 7.4.7).

Peyton Manning was moving towards the line to call an audible when the ball...

Generally penalties can be declined. Though you mostly don't want to decline them.

Refusal of Penalties. Unless expressly prohibited, the penalty for any foul may be declined by the offended team, and play proceeds as though no foul had been committed. The yardage distance for any penalty may be declined, even though the penalty is accepted. (NFL rulebook p76)

The noted exception here is the double foul. Which cannot be accepted or declined as they typically offset.

However, certain penalties, mostly of the pre-snap kind on the offense, mean that no play took place (play is blown dead prior to the snap) and not accepting the penalty means that the down is replayed at the same spot on the field rather than 5 yards further back. That means that you don't want to decline them, and you're stuck accepting them or not getting any benefit at all.

So basically in this instance, if the penalty is declined, it would be the same situation again as the missed...

In sports, a false start is a movement by a participant before (or in some cases after) being signaled or otherwise permitted by the rules to start. Depending on the sport and the event, a false start can result in a penalty against the athlete's or team's field position, a warning that a subsequent false start will result in disqualification, or immediate disqualification of the athlete from further competition.

False starts are common in racing sports (such as swimming, track, sprinting, and motor sports), where differences are made by fractions of a second and where anxiety to get the best start plays a role in the athletes' behavior.

A race that is started cleanly, on the contrary, is referred to as a fair start or clean start.

In sports[edit]

American and Canadian football[edit]

In American football and Canadian football, a false start is movement by an offensive player (other than the center) after he has taken a set position. For...

BIRMINGHAM, England The danger of one inadvertent twitch ruining the greatest day of a sprinter's life has been removed after athletics' governing body softened the rules on false starts ahead of the London Olympics.

The little-publicized clarification by the International Association of Athletics Federations (IAAF) permits athletes to move in the starting blocks without being disqualified so long as their hands do not leave the ground or their feet the blocks.

Previously, such twitching or flinching could have resulted in disqualification at the discretion of the starter.

"The bottom line is, outside of an athlete removing his hands off the track or his feet leaving the blocks, nothing else is a false start," David Katz, one of 17 members on the rule-making IAAF technical committee, told Reuters by telephone.

The need for improved quality and consistency by starters worldwide had prompted the clarification, said Paul Hardy, IAAF competitions...

Definition

It is a False Start if the ball has been placed ready for play, and, prior to the snap, an offensive player who has assumed a set position charges or moves in such a way as to simulate the start of a play, or if an offensive player who is in motion makes a sudden movement toward the line of scrimmage. Any quick abrupt movement by a single offensive player, or by several offensive players in unison, which simulates the start of the snap, is a false start. Exceptions: This does not apply to an offensive player under the center who turns his head or shoulders, unless the movement is an obvious attempt to draw an opponent offside.

Outcome

Loss of five yards from the line of scrimmage. The foul is enforced prior to the snap.